400 ON THE CHANGE OE1 REFRANGIBIUTY OF LIGHT. to the supposition that the production of light, of chemical changes, and of phosphoric excitement, are merely different effects of the same cause. The phosphorogenic rays of an electric spark, which, as is already known, are intercepted by glass, appear to be nothing more than invisible rays of excessively high refrangibility, which there is no reason for supposing to be of a different nature from rays of light. NOTES ADDED DURING PRINTING. Note A. Art. 23. Shortly after the preceding paper was forwarded to the Royal Society, I found M. Edmond Becquerel's map of the fixed lines of the chemical spectrum, which is published in the 40th volume of the Biblioth&que Universelle de Geneve (July and August, 1842). I had seen in Moigno's Repertoire d'Optique Moderne, that the map had been presented to the French Academy, and naturally felt anxious to obtain it; but not finding any further notice of it either in that work or in the Comptes Rendus, I supposed that it had not yet been published. The principal lines in this map I recognized at a glance. M. Becquerel's broad band / is my I; his group of four lines M with the preceding band forms my group m ; his group of four lines N forms the first four of my group n; his line 0 is my n. It is only in the last group that there can be any doubt as to the identification; but I feel almost certain that M. Becquerel's P is my o, and the next two lines, the last in his map, are the two between o and p. It is difficult at first to believe that the strong line p should have been left out, while tin* two faint lines between o andp are represented, but the difficulty is, I think, removed by considering the feeble photographic action in that part of the spectrum. M. Becquerel expressly states that lines were seen beyond the last he has represented, though they were hardly distinct; and on comparing together his map, Mr Kingsley's photographs, and my own map, I think hardly any doubt can remain as to the identification.